In numerous high temperature applications control devices are required to switch between various states at given temperatures, or temperature ranges. These devices may be active or passive. An example of a passive low temperature device is an automotive thermostat, which typically operates below 130° C. These thermostats may utilize wax pellets whose composition is chosen for the temperature range to be served. Other passive devices may include bimetallic strips, whose temperature affected shape change is utilized to facilitate a physical actuation.
These designs are only viable at low temperature. Currently, there are no passive, high temperature thermostats capable of applying sufficient mechanical force with reliable operation above approximately 200° C. Bimetallic thermostats are most often used with active electronic control where the bimetallic elements close contacts for an electric circuit. There is a need for a thermostatic control device that is operable at higher temperatures and is capable of providing sufficient actuation force.